"It became clear that we failed to fulfill what I consider one of our most important responsibilities -- to communicate our intentions clearly. I am sorry for that, and I am focused on making it right," Systrom wrote on Instagram's blog tonight. "Because of the feedback we have heard from you, we are reverting this advertising section to the original version that has been in effect since we launched the service in October 2010."

The clause users were most concerned with was one that implied Instagram would allow users' photos to appear or be displayed in advertisements. Systrom cleared up that concern.

"I want to be really clear: Instagram has no intention of selling your photos, and we never did. We don't own your photos -- you do," he said.

After hearing of the new terms, many users were up in arms and said they planned to quit the service (including a few in Hollywood). Even after Systrom's original response, National Geographic and other large brands said they would reevaluate their use of the service.

"Instagram needs to do some serious damage control to repair what was a pristine, 'for the users' brand," Patrick Moorhead, principal analyst at Moor Insights & Strategy, told ABC News.

Regardless, Instagram, which Facebook bought for $1 billion, will begin to start advertising. It just might do it in some different ways.

"Going forward, rather than obtain permission from you to introduce possible advertising products we have not yet developed, we are going to take the time to complete our plans, and then come back to our users and explain how we would like for our advertising business to work," Systrom said.

"Instagram, like all mobile properties, needs to drive revenue and they will turn to advertising," Moorhead said. "This will turn away some users at first but, like Facebook and Twitter, users will adjust and not flee en mass."